194 



NATURE 



[November 8, 191 7 



OUR ASTRONOMICAL COLUMN. 



The Meteoric Shower of October.— Between 

 October 13 and 28 last, inclusive, observations were 

 obtained at Bristol on fourteen jiights, and 197 meteors 

 were seen in tVi^enty-three hours of watching, chielly 

 before sunrise. Fifty-six of the meteors recorded be- 

 longed to one or other of the two principal displays 

 of the October epoch near § Geminorum (98°+ 14^, 

 thirty-two meteors) and v Orionis (92*^+15°, twenty- 

 four meteors). The former was also the stronger 

 shower in 1916, and in some previous years, though in 

 1877 and 1887 the Orionids formed by far the richer 

 display. Of the minor showers the most active were 

 -at 42"' + 20° in Aries, .and 163° + 59° near /3 Ursae 

 Majoris. 



Two fireballs have been recently observed with suffi- 

 cient completeness to -allow their real paths to be 

 ascertained, viz. : — 



(i) October i8,-2h. 15m. a.'m., radiant 9o° + i6°, 

 height seventy-two to forty-seven miles over Lincoln- 

 shire. 



(2) October 23, 7h. 33m. p.m., radiant 42° + 20°, 

 height sixty-five to thirty-three miles from over North 

 Sea to west of Scarborough. 



Galactic Condensation of Stars. — -Expressing 

 galactic condensation as the ratio of the number of 

 stars per unit area at 5° galactic latitude to the num- 

 ber at 80°, Kapteyn found values ranging from 2-8 at 

 the ninth magnitude to 27-7 at the sixiteenth. The 

 relatively large value for the very faint stars did not 

 appear in Chapman and Melotte's discussion of the 

 Franklin-Adams plates, but it has since been substan- 

 tially confirmed by work with the 60-in. reflector at 

 Mt. Wilson. A further investigation of this question 

 has been based by Dr. F. H. Seares on the counts of 

 nearly 600,000 stars which have been collected by 

 Prof. Turner {Astrophysical Journal, vol. xlvi., p. 117). 

 The galactic condensation deduced from these is in 

 close agreement with the results obtained by Kapteyn. 

 The variations of density with right ascension, how- 

 ever, are not greater than the uncertainties affecting 

 the results, so that no evidence was found for the 

 spiral of obscuring matter derived by Prof. Turner 

 from the same data. It would appear that Prof. 

 Turner did not make sufficient allowance for the high 

 galactic concentration of the faint stars. 



The Variability of B.D. +56547°. — The variability 

 of this star was first detected by Mr. J. Van der Bilt, 

 and, at his suggestion, the photographic magnitudes 

 have been determined by Messrs. Martin and Plummer 

 from numerous plates taken at Dunsink in connection 

 with a previous study of three other variables in the 

 region of x Persei (Monthly Notices, RiA.S., vol. Ixxvii., 

 p. 651). The star has turned out to be of rather special 

 interest, inasmuch as it shows an unexpected 

 periodicity. The interval from maximum to maximum 

 is about 704 days, and the range of variation is from 

 Tnagnitude 9-8 to 10-3. The other three stars resemble 

 it in having a high colour-index, and are therefore 

 probably in a similar physical condition, but these vary 

 in the irregular way which is characteristic of nearly 

 all variables which are very red. 



The " Journal des Observateurs." — The index to 

 vol. i. and the first -number of vol. ii. of this publica- 

 "tion have been received. The journal is especially 

 noteworthy for communications relating to observations 

 and ephemerides of minor planets and comets. The 

 current issue gives ephemerides of the planets (108) 

 Hecuba and (394) Arduina, together with observations 

 of numerous planets made at Nice, and of Mellish's 

 comet (iQjya) made at the Cape Observatory. The 

 ■editor is M. Henry Bourget, director of the Observa- 

 torv of Marseilles. 



A' 



MILITARY AIRCRAFT AND THEIR 

 ARMAMENT, 



N article of considerable interest, under the title 

 of "La Technique Allemande de I'Armement 

 Aerien," appears in La i\ature for October 6 by Jean- 

 Abel Lefranc. The author traces out the development 

 of German aerial warfare, with particular reference 

 to the armament of military aircraft. Victory in the 

 air, he says, depends on two sets of factors — tactical 

 and technical. Under the former head he places 

 favourable time of attack, good position, powerful 

 formation ; under the latter, armament, speed, flexibility 

 of control, and altitude. To secure a good tactical 

 position a machine must possess good technical factors ; 

 for instance, good armament is useless unless a 

 machine is fast enough to be able to challenge the 

 enemy to battle. Nevertheless, the pilot counts for a 

 great deal, and the " Farmans " of 1915 beat the 

 ■' Aviatiks,". although the latter were faster, better 

 armed, and more flexible. M. Lefranc remarks that 

 the relative importance of the technical elements de- 

 pends on the purpose of the machine; for a battle- 

 plane, he places them in the order speed, flexibility, 

 armament, and altitude. The last attribute might be 

 omitted, since a fast machine is always a good climber 

 unless the landing speed is abnormally high. For 

 slow and heavy machines designed for bombing, a 

 powerful defensive armament is most essential. For 

 night raiders radius of action, bomb capacity, and 

 facility of landing are more important than armament. 

 The speed of both French and German fighters varies 

 from 100 to 120 miles per hour. These speeds could 

 be higher but for the necessity of a reasonable landing 

 speed and a good climbing rate. The heavy bombing 

 machines fly at speeds from eighty to ninety-five miles 

 per hour. Flexibility nas now developed almost with- 

 out limit. 



M. Lefranc divides the period since the war com- 

 menced into two parts. In the early days the import- 

 ance of the mastery of the air had not been fully 

 appreciated, and aerial combats were rare. The chief 

 use of aeroplanes was to obtain information as to the 

 enemy's position. The French machines, being of the 

 "pusher" type, mounted the gun in front, and had a 

 large " dead angle " behind, which was out of the range 

 of fire of the gun. The German machines were mostly 

 tractors and mounted their guns behind the main 

 planes. They had the decided advantage that their 

 "dead angle" was under the surveillance of the pilot. 

 Early aerial fights were generally ineffective, and re- 

 sulted in a few bullet-holes in the wings, mainly owing 

 to difficulties of aim and the small quantity of ammu- 

 nition carried. 



The later period of the war has produced three main 

 types. The first type resulted from the design of a 

 gun firing through the propeller and under the control 

 of the pilot. Firing through the propeller may be 

 achieved by fitting metal shields to the blades to pre- 

 vent destruction by the bullets, but is better attained 

 by automatic timing of the firing to miss the blades, 

 as this need not interfere with the design of an efficient 

 propeller. The second type, a heavier machine, mounts 

 a rear gun on a turntable, in addition to that firing 

 ahead through the propeller. In the third type, of 

 which the 1916-17 Gotha is an example, twin pro- 

 pellers are used, and both forward and rear guns have 

 a wide angle of fire. There is also a third gun firing 

 below the fuselage, as a defence against attack from 

 below — a very vulnerable point in the older machines. 

 This third type has no " dead angle," but can bring 

 one or other of its guns to bear on any point. One 

 of the greatest difficulties of effective gun practice in 

 the air is that due to error of aim resulting from the 

 relative movement of the two machines. Various 



NO. 2506, VOL. 100] 



